1. Field of the Invention
The invention relates to a process for searching patterns for the purpose of positioning or the like in an exposure for the production of semiconductor components, printed boards, liquid crystal displays, printer heads of the inkjet type, multichip modules and the like process, and also for determining the marks in a chip mounter, a bonder, a probing tester and the like and for similar purposes. The invention furthermore relates to a device for positioning of a mask to a workpiece. The invention relates especially to a process for searching patterns, a process which is suitable for determining marks on a workpiece with a rough surface, and a device for positioning of a mask to a workpiece. In particular, to such a device which can be used, not only for searching patterns on a semiconductor substrate, but also for searching patterns on a ceramic substrate, a metal and a thin metallic plate, a printed board, a glass substrate which is not polished to a high gloss, and the like.
2. Description of Related Art
Production of semiconductor components, printed boards, liquid crystal displays, printer heads of the inkjet type, multichip modules and the like includes an exposure process. In this exposure process, it is important in the transfer of the mask pattern onto the workpiece that another pattern to be subsequently transferred is exactly positioned relationship to a pattern which has been formed beforehand. The above-described positioning is conventionally done such that the alignment marks which are recorded on the mask and the workpiece come to rest on top of one another.
FIG. 7 schematically shows the arrangement of a device for determining the alignment marks on a workpiece. In the drawings reference letters AU indicate an alignment unit which consists of a half mirror M, lenses L1, L2 and CCD camera 11. Furthermore, reference number 12 identifies a monitor and numeral 13 an arithmetic-logic unit. The workpiece on which alignment marks AM are projected or recorded is designated W.
In the following, a pattern search of alignment marks AM on workpiece W is described using FIG. 7.
First, alignment marks AM are recorded in arithmetic-logic unit 13. For example, cross-shaped marks as in FIG. 8(a) are used as alignment marks AM. In arithmetic-logic unit 13, patterns of alignment marks AM are recorded, in which monitor pixels are regarded as unity, as is illustrated in FIG. 8(b). In the figure, the number of pixels is set to a 5.times.5 matrix to facilitate the explanation.
Next, as is shown in FIG. 7, illumination light is transmitted via the half mirror M of alignment units AU onto alignment marks AM on workpiece W. Alignment marks AM are picked up by CCD cameras 11, one of which is depicted in FIG. 7. Furthermore, images of alignment marks AM which have been projected onto monitor 12 are input into arithmetic-logic unit 13 and converted into coordinate data, the pixels of the monitor being considered unity. In arithmetic-logic unit 13, the above described recorded patterns are compared to the images of the picked-up alignment marks.
The case in which the images of the picked-up alignment marks (searched patterns) correspond to searched pattern A in FIG. 8(c) is recognized as score 60 because agreement with the recorded pattern is around 60%.
The case in which the images of the picked-up alignment marks (searched patterns) correspond to searched pattern B in FIG. 8(d) is recognized as score 80 because agreement with the recorded pattern is around 80%.
The case in which the images of the picked-up alignment marks (searched patterns) correspond to searched pattern C in FIG. 8(e) is recognized as score 100 because agreement with the recorded pattern is around 100%.
When patterns with a score of roughly 100 are recognized, these patterns are recognized as searched patterns, as was described above.
In the production of semiconductor components and the like, for purposes of cost reduction and the like there are cases in which an etched wafer which has not undergone high gloss polishing is used, when a pattern is formed on the wafer with a line width which is not extremely fine (surface roughness is different depending on the users).
FIG. 9 schematically shows one example of an image of the above described wafer which has not undergone high gloss polishing. As is shown in the drawing, in the case of a wafer which has not undergone high gloss polishing, images with prominent contrasts occur as a result of surface roughness such that they and the image of the alignment mark come to rest on top of one another, or that they are located on the periphery hereof.
If, when the alignment marks which are located on a wafer of this type are recognized, the above described pattern search method is undertaken, the above described images as a result of surface roughness are sent as signals with prominent contrasts from the CCDs camera and the image signals of the searched patterns of the images due to surface roughness are added to the coordinate data of the searched patterns. As a result, the score decreases, and a pattern search can no longer be done.
This also applies in workpieces besides the above described wafer which has not been subjected to high gloss polishing. In the above mentioned ceramic substrate, metal and the metallic thin plate and the like, there are a host of cases in which a search of the alignment marks by the above described pattern search process is difficult to perform.